Create rule packs

Functions for creating different kinds of rule packs. Rule is a function
which converts data unit of interest (data, group, column, row, cell) to
logical value indicating whether this object satisfies certain condition.
Rule pack is a function which combines several rules into one functional
block. It takes a data frame of interest and returns a data frame with
certain structure and column naming scheme. Types of packs differ in
interpretation of their output.

Value

Details

These functions convert ... to list, apply rlang's
squash() and add appropriate classes (group_packs() also
adds necessary attributes). Also they are only constructors and do not check
for validity of certain pack. Note that it is allowed for elements of
... to not have names: they will be computed during exposure. However it is
a good idea to manually name packs.